136 



SAMPLING MILK AND CREAM 



operators realize that, while these samples are waiting for the 

 tester, they are subject to rapid deterioration and to changes 

 in composition due to evaporation of moisture, which has a 

 disturbing influence upon the accuracy of the test. In many 

 creameries the samples are allowed to remain on the shelves 

 of the receiving platform without protection from heat and 

 exposure to air. Careful observations have shown that there 

 is a strong tendency on the part of the cream samples, kept un- 

 der these conditions, to increase in per cent of fat with age. 

 This is due to the escape of moisture from the cream by evap- 

 oration. The rapidity with which this evaporation takes place 

 depends on the tightness or looseness of the seal of the sample 

 bottles and on the temperature of the place where they are 

 stored. This fact was demonstrated in a brief experiment con- 

 ducted by the writer, in which the daily shipments of cream 

 from six patrons were sampled for single tests and for com- 

 posite tests. Each patron's sample was divided among nine 

 bottles, three of which were tightly sealed, three loosely sealed 

 and three were left open.' One set of these bottles from each 

 patron was placed in the ice box at a temperature of 50 de- 

 grees F., one set was left on the receiving platform and one set 

 was placed near the boiler at a temperature of 90 to 110 de- 

 grees F. The results are shown in the following table : 



Table 23. Per Cent Fat of Cream Samples Kept in Bottles Sealed 

 Tightly, Loosely and Left Open, at Different Temperatures. 



